The objective of the study is to provide insight into ways in which mammary epithelial-stromal cell interactions influence estrogen and/or progesterone-induced proliferation in normal mouse mammary gland. Of particular interest is to determine how stromal influences can affect hormone independence in normal and cancerous mammary tissue. The relationship between epithelial-stromal interactions and hormonal regulation will be analyzed both in vivo and in vitro by comparing different mammary gland development stages that exhibit varying degrees of hormone independence. In all cases proliferation will be assessed in epithelial and stromal cells by DNA histoautoradiography. The effects on hormone receptor regulation will be monitored by ligand binding assays, steroid autoradiography, or immunocytochemistry using anti-hormone receptor antibodies. From in vivo experiments we intend to determine if estrogen and/or progesterone are direct acting mitogens or if they act indirectly via local paracrine or autocrine growth factors or systemic growth factors such as epidermal growth factor or transforming growth factors. We will determine if estrogen and/or progesterone induced proliferation are correlated with the presence of estrogen or progesterone receptors in epithelial cells or stromal cells. We will also determine if one can alter hormonal responsiveness in vivo by manipulating the stromal environment. From in vitro, cell culture studies we intend to identify cellular, biochemical and molecular mechanisms by which stromal cells affect hormone responsiveness. Epithelial cells and stromal cells will be physically separated from one another and further dissected into their biochemical and molecular components. Reconstitution will be experimentally manipulated to identify the specific types of stromal cells involved, the roles of cell contact and soluble factors in hormone dependent proliferation. The biochemical composition of the extracellular matrix has a profound effect on hormonally regulated gene expression of milk proteins. Similar biochemical and molecular methods will be applied to the study of extracellular matrix and proliferation. The long term goal of these studies is to elucidate the biological basis of hormone independence and provide a rationale for treatment of hormone independent human mammary cancer.